The invention concerns a tunnel for cooling, heating, or drying products of the foodstuffs and especially confectionery industries, with a base, especially one comprising several adjacent segments, with a series of self-supporting hoods that have a cross-section in the form of an inverted U and are made of rigid expanded plastic, with tracks between the edges of the base and the walls of the hoods to create a seal, and with a belt to convey the products longitudinally through the interior of the tunnel. The particular interior design of the tunnel, the number and distribution of channels, that is, with air or water flowing through them, especially for cooling purposes, is of subordinate importance to the invention, which is much more concerned with the design and distribution of the walls of the tunnel, which can consist either of a continuous base or of several adjacent segments, whereby the base is covered by a series of hoods such that the interior of the tunnel is enclosed along the direction that the conveyor belt travels in.
A tunnel of this type is known from European Exposure 144 456. Since the hoods are moldings of rigid expanded plastic, especially polyurethane, they are self-supporting units that cover the base of the tunnel. For sealing purposes there is a track in the vicinities of each wall of every hood and of the base. The tracks comprise a continuous tenon on the base that fits into a matching mortise in the free edge of the wall of the hood. The track is continuous along the length of the hoods and hence over the total length of the tunnel. The track seals the tunnel off longitudinally. Transversely, a seal that extends over the U-shaped cross-section is inserted into at least each face of every hood. The hoods are forced together by longitudinal tensioning mechanisms, making the tunnel tight transversely as well by way of the inserted seals. The faces of the hoods are not covered.
The inside of any tunnel, especially a tunnel employed in the confectionery industry, must be cleaned from time to time, and it is the base and the various built-in apparatus--cooling surfaces, baffles, etc.--that the process may concern in particular. The labyrinth-like channel in the vicinity of the track also requires cleaning. This necessity occurs basically because particles of chopped nuts, puffed rice, rolled oats, etc. that have been sprinkled over the products traveling through the tunnel fall off onto the conveyor belt and accumulate inside the tunnel. The same events occur with particles that contain fat--slivers of chocolate and other constituents for example that drop off the products while they are traveling through the tunnel and even through the belt, which is often in the form of a mesh, into the tunnel. These greasy particles become rancid inside the tunnel after a while. Particles of dust entrained by the cooling air etc. can also make it necessary to clean the tunnel from time to time. Otherwise, the requisite health conditions will not exist. It may, however, also be necessary to look inside the tunnel from time to time to monitor the products and even to obtain samples. It is in any case very important for the inside of such a tunnel to be easily accessible, at least for cleaning purposes.
The tunnel known from European Exposure 144 456 has spreaders made of mutually articulated arms or brackets between each hood and its associated base. Each hood can accordingly be lifted off the base and positioned above the conveyor belt to provide access to the interior. Obviously the axial and longitudinal tension on the hoods must be released before one or more can be lifted. Since the hoods are not covered, however, each hood can to advantage be lifted independently of its adjacent hoods and maintained in the lifted position by the spreaders. The space inside the tunnel accordingly becomes accessible to advantage from each side. This bilateral accessibility is very important because such a tunnel may be as much as two meters wide and can accordingly not be effectively cleaned from one side alone. A drawback is that two operators must cooperate to lift the hoods. The distribution, design, and operation of the spreaders are also not without problems. These mechanisms are usually made of metal and must initially be mounted on the hoods, which are made from rigid expanded plastic. Metal parts are always a drawback for thermodynamic reasons in a tunnel of this type. Even the conventional anchoring of the spreaders in the plastic that the hoods are made of is not simple. For tunnels that are not very wide it is completely satisfactory for the hoods to fold up at only one side to allow access for cleaning from the opposite side. This, however, is impossible with the known hoods which can only be lifted straight. For many purposes it would also be a good idea to be able to completely remove the hoods from the base.
This as well, however, is impossible in this case without removing the spreaders.
Also known is a tunnel wherein both the segments of the base and the hoods are made of rigid expanded plastic and have no metal parts. This tunnel is also sealed tight by a track between the base segments and the hoods. The track does not extend far enough across the horizontal plane to act as a hinge. It only constitutes a labyrinth seal for the inside of the tunnel. Hence, although the hoods can be removed from the base of the tunnel, they cannot be tilted up. The removability provides satisfactory access from both sides of the tunnel as is desired for cleaning purposes. During such cleaning, however, the hoods must be accommodated somewhere, on an adjacent hood that has not been removed yet or on the floor for example. Since no metal parts are involved in this embodiment, the hoods are advantageously light in weight and their surface is unobjectionable in that it is easy to keep clean and has no angles or corners that could harbor bacteria. The walls of the tunnels are also thermodynamically optimal because there are no metal parts to short the heat. The base segments and hoods are easy to manufacture. Once they have been expanded, they need no further processing and there are no metal components to be mounted. There is a drawback to this known tunnel in that they hoods cannot be pivoted up at one side and must always be completely removed. Once they have been removed they can to a certain extent be exposed to damage.
Also known is a tunnel with hoods made at least partly of metal. The metal components can comprise a framework with plastic foamed around it to satisfy thermodynamic demands. Using enameled sheet steel for the inner and outer surface of the hood and filling the space between the surfaces with foam is also known. This type of hood does have a covering in the vicinity of the face that is useful for sealing purposes, although this is accompanied by the drawback that only every other hood can be tilted up independently of the adjacent hoods. The hoods are also provided with hinges along one side of the tunnel, in the vicinity of one arm of the U-shaped cross-section. These hoods can accordingly be pivoted up only from one side, so that, when the tunnel is wide, it can no longer be cleaned from the side where the hinge is. Furthermore, the hoods cannot be removed, which is another drawback. Since the metal parts make the hoods substantially heavier, they are harder to pivot up. Once they have been pivoted up, however, they are protected from damage. These hoods are complicated and expensive to manufacture and the hinges are difficult to mount.